240 CHARLES S. RIDGWAY 



Some of the probable advantages of the method are the ease 

 and low cost with which it may be operated, the avoidance of 

 complicated, costly and frequently unreliable mechanisms, and 

 the reduction of error due to the personal factor in observation, 

 so prominent in the photographic paper method. The chief 

 values of the chemical photometer, however, if its reliability is 

 established, will lie in the facility with which several exposures 

 may be made simultaneously under various degrees of illumina- 

 tion and the fact that the solution gives an automatic integra- 

 tion for the time period of exposure. The automatic exposure 

 of vessels containing light sensitive solutions by the use of clocks 

 has been accomplished by Stone*^ and a similar arrangement 

 may be advantageous in connection with the one just described. 

 Though plans are made for further work with the oxalic-acid- 

 uranium-salt photometer during the coming growing season, 

 it is hoped that it will be carefully investigated in its application 

 to problems in plant physiology, especially with reference to the 

 correlation of its properties with the various life processes, 

 since such research, though attractive, lies without the province 

 of the writer in his present field of activity. 



^ Stone, G. E., The relation of light to greenhouse culture. Mass. Agri. 

 Expt. Sta. Bull. 144, July, 1913. Though the results of measurements of light 

 by a photochemical method are stated, the details of the method are not given. 



